1. Field of the Invention
The invention relates to filters for photo-detectors, where the filters are permeable to that spectral range of electromagnetic radiation which lies in the operating range of the associated photodetector, and are largely impermeable to other spectral ranges.
2. Description of the Prior Art
Semiconductor detectors generally exhibit a wide sensitivity range, of which, however, frequently only a narrow spectral range is employed as an operating range. The sensitivity range of semiconductor detectors, which lies outside the operating range of the detector, gives rise to undesired interference currents under the influence of foreign light. Therefore, in order to reduce these interference currents, it is desirable to provide semiconductor detectors with optical filters which are impermeable to electromagnetic radiation in the entire sensitivity range of the detectors, excluding their operating range. A measure of this type could be readily effected employing commercially available optical filters. However, in a mass production of optical semiconductor components, important factors oppose the use of commercially available filters. As is known, optical filters are expensive which would lead to a considerable increase in the cost of the end product. The costs of the filter assembly would also constitute another, not inconsequential increase in the cost for the end product. Thus solely for economical considerations, it is not advisable to equip photo-detectors with commercially available filters.
The use of pre-manufactured, optical filters in photodetectors also restricts the technical possibilities for use, since only a specific assortment of filters having specific technical characteristic parameters and specific shapes and sizes are available. Any deviation from the predetermined characteristic data and the predetermined dimensions would at least increase the costs of, if not render impossible, the use of pre-manufactured filters.